Hitherto, circuits shown in FIG. 15 and FIG. 16 are known as examples of a circuit in which an earth leakage breaker and a lightning arrester are connected to each other in order to protect electrical machinery and apparatus from a lightning surge.
In the drawings, reference numeral 1 is an electric path, numeral 2 is an electrical machinery acting as a load, numeral 3 is a lightning arrester, and numeral 4 is an earth leakage breaker. The earth leakage breaker 4 is comprised of a contact 41 for switching on/off the electric path 1, a switch mechanism 42 composed of a toggle link mechanism for opening and closing the foregoing contact 41, an overcurrent detector section 43 composed of an electromagnetic device including a bimetal for detecting an overcurrent of the electric path 1, oil dashpot or the like, a zero phase current transformer 44 for detecting a current leakage of the electric path 1, and a leakage trip circuit 45 for determining an output level of the zero phase current transformer 44. When detecting an overcurrent of the load 2 or current leakage of at least a predetermined level of a load circuit is detected, the earth leakage breaker 4 releases the switch mechanism 42 from a closed state, and the switch mechanism 42 opens the contact 41 in order to interrupt an electric current to the load 2.
In the connection arrangement shown in FIG. 15, the lightning arrester 3 is connected between the earth leakage breaker 4 and the load 2. A lightning surge that invades from the power supply is guided through the overcurrent detector section 43 and the zero phase current transformer 44, and is absorbed by the lightning arrester 3. If the invading lightning surge is of a large energy, the lightning arrester 3 is short-circuited by the energy, and the overcurrent detector section 43 detects a short circuit current of the electric path 1 due to the short circuit and opens the contact 41 in order to prevent a short circuit accident.
It is a recent trend to employ the earth leakage breaker 4 in which the leakage trip circuit 45 is resistant to a lightning surge and capable of preventing a malfunction by discriminating a detected waveform. However, in such an earth leakage breaker, even in case of a lightning surge not so large as to short-circuit and break the lightning arrester 3, an electric current flows to an earth through the lightning arrester 3 and is detected by the leakage trip circuit 45, thereby erroneously occurring an earth leakage breaking operation.
The leakage trip circuit 45 resistant to a lightning surge and capable of preventing a malfunction determines a waveform peculiar to the lightning surge. In some cases, however, during the propagation of waveform through a distribution line, a waveform change may take place from the waveform peculiar to the lightning surge due to line constant of the distribution line and others, whereby an earth leakage breaking occurs erroneously. Such a malfunction of the earth leakage breaker 4 causes a power failure of the load 2, which results in trouble and bothers on the part of electricity users.
In the connection arrangement shown in FIG. 16, the lightning arrester 3 is connected between the power supply and the earth leakage breaker 4. In the connection of this type, a lightning surge of a level at which the lightning arrester 3 works is absorbed by the lightning arrester 3 itself and is not inputted to the earth leakage breaker 4. On the other hand, if the invading lightning surge is of a large energy, a power supply short circuit accident may occur due to damage of the lightning arrester 3, and therefore the connection arrangement in FIG. 16 is not recommendable.
As described above, in the conventional connection of the lightning arrester to the earth leakage breaker, a problem exists in that it is impossible to prevent both malfunction caused by a lightning surge and occurrence of a power supply short circuit accident.
The present invention was made to solve such a problem and provides an earth leakage breaker capable of preventing a malfunction of the earth leakage breaker caused by a lightning surge and preventing a short circuit accident when the lightning arrester is short-circuited and broken by a lightning surge of high level.